Studies on interaction between gatifloxacin and human serum albumin as well as effect of copper(II) on the reaction

The binding characteristics of gatifloxacin (GTFX) and human serum albumin (HSA) have been studied by fluorescence spectroscopy in aqueous solution, and the interaction influenced by copper(II) was also explored in the paper. The results show that the two-reaction equilibrium constant and the number of binding sites were K = 1.16 × 105 l mol−1, n = 1.27 for GTFX and K = 1.62 × 105 l mol−1, n = 1.74 for GTFX-Cu2+, respectively. The quenching mechanism of fluorescence of HSA by GTFX is a static quenching procedure. The binding distance between GTFX and HSA and the energy transfer efficiency are obtained based on the theory of Fōrster spectroscopy energy transfer. The effect of GTFX on the conformation of HSA was also been analyzed by using synchronous fluorescence spectroscopy. The interaction of GTFX and HSA has been studied by flow-mixed microcalorimetry in the absence and presence of copper(II) and their thermodynamic parameters were obtained. The enthalpy changes and the entropy changes were calculated to be ΔH ≈ 0, ΔS > 0 in the absence of copper(II),which indicated that static forces played major role in the interaction of GTFX and HSA, and to be ΔH ≈ 0, ΔS > 0 in the presence of copper(II),which indicated that the static forces also played major role on the reaction. The molar free energy changes of the two reactions are identical with each other because the entropy-enthalpy compensation happened between the two reactions.